September is usually a month when the atmospheric concentrations of carbon dioxide (CO2) are at their lowest levels in the northern hemisphere. That’s because plants suck up a lot of the gas as they grow during the summer. But this year, the level of the greenhouse gas has remained stubbornly above the symbolic “red line” of 400 parts per million. This has caused scientists to predict that CO2 levels will not return to environment-friendly levels "ever again for the indefinite future.”
It is, therefore, no wonder that experts worldwide are frantically trying to come up with innovative “carbon capture and storage” (CCS) solutions. Previous attempts have included pumping the gas into solids like sandstone or salty aquifers. However, these are not foolproof given that the gas could easily leak, or, worse, explode into the atmosphere. It is also expensive because the CO2 has to be separated from the other gases emitted by industrial plants.
Now, a team of researchers led by Columbia University professors Juerg Matter and Martin Stute, have a new solution: converting CO2 into stone! The impetus for the radical idea came in 2006 after the President of Iceland approached the university researchers for ideas to reduce the nation's already low gas emission rates even further.
It took six years for the Columbia researchers and scientists from the Universities of Copenhagen and Iceland to come up with a feasible solution. To implement the pilot program they teamed up with Iceland’s Hellisheidi power plant, the world’s largest geothermal facility. The plant, which uses volcanically-heated water to run electricity-generating turbines, produces few emissions. However, pumping underground water releases volcanic gases, including, carbon dioxide and the foul-smelling hydrogen sulfide, into the atmosphere.
The CarbFix project entailed mixing the CO2 with water and pumping it 1,500-feet underground into the basalt – the volcanic rock that makes up 90% of the ground beneath Iceland. The acidic solution interacts with the calcium, magnesium, and iron ions present in the rock to form environmentally benign carbonate minerals.
Matter says the results of the 2012 pilot program were even better than the team had anticipated. Over 95 percent of the 220 tons of CO2 pumped into the basalt converted to limestone in two years, significantly faster than the hundreds or thousands of years it normally takes! To ensure that the element remained safely stored, the team tracked the rocks with carbon-14, a radioactive form of CO2. Sure enough, they found that nothing leaked back up to the surface. Encouraged by the results, this year, the researchers plan to bury 10,000 tons of CO2 — about one-fourth of Iceland’s annual carbon emissions.
The researchers, who published the ground-breaking results in Science Magazine in June 2016, have received numerous inquiries about the technology from other geothermal companies. Sigurdur Gislason, a University of Iceland geologist and the study’s co-author, believes that the biggest beneficiaries of the technology would be fossil-fueled powered plants and other heavy industries, who are responsible for the bulk of the emissions.
However, there are a few challenges that need to be addressed before CarbFix can be widely adopted. In addition to needing easy access to volcanic rock, the technology also requires large amounts of water. That’s because it takes 25 tons of water to bury each ton of CO2. Given that seawater can also be used, that hurdle can be overcome for industries situated close to the ocean. Also, similar to other CCS techniques, there is a steep cost associated with separating the CO2 from the other gases that are in the mix. In the case of Iceland’s Hellisheidi power plant, the scientists have managed to keep the costs low by using existing infrastructure to pump the CO2 underground. They also, have not bothered to extract the minor amounts of hydrogen sulfide, mixed in with the CO2.
However, CCS expert Christopher Rochelle at the British Geological Survey believes that while CarbFix may not be commercially applied anytime soon, the discovery is a significant step forward. It demonstrates the importance of real-world experiments, instead of modeling theories and hypothesis in labs.
Fortunately, CarbFix is not the only innovative project in the works to try to reduce the increasing levels of the greenhouse gas. Exxon Mobile is working on an experiment to build fuel cells that turn CO2 into energy, while US car manufacturer Ford is attempting to convert the gas emissions to solid foam that can be used to make the interior of vehicles. In Oman, a separate effort is underway to pump the emissions into peridotite rock that may react even more rapidly with CO2 than basalt. But even if all these projects are wildly successful, the only long-term solution to reversing climate change is to adopt widespread green energy initiatives. Hopefully, governments and corporations worldwide will go the extra mile to make that a reality soon.
Resources: sciencemag.com, wired.com, phys.org